Various processes are known by which a filament yarn is provided with bulkiness.
According to one process, a multifilament yarn is subjected to a false twisting and twists running back along the yarn are heat set, and then the false twisted filaments are opened so that a so-called woolly type yarn is produced. Although such a woolly type yarn is bulky enough, it does not have an appropriate bending resiliency.
According to another process, a so-called Taslan (Registered Trade Mark owned by Du Pont de Nemours) yarn is produced by wrapping a wrapper yarn about a core yarn by means of a fluid nozzle. However, since such a Taslan yarn has a stiff core portion, it has an inferior hand.
Furthermore, the above-mentioned woolly type yarn and Taslan yarn require an additional step for false twisting the yarn and for fluid treating the yarn, respectively, and accordingly, the manufacturing processes are complicated.
In a still another widely utilized process, yarns having different shrink properties are first mixed. Then, the mixed yarns are subjected to a heat treatment in a dyeing and finishing process after the mixed yarns are woven into a fabric so that a difference in shrinkages is created and so that the bulkiness of the fabric is increased. However, since this process relates to a spontaneous contracting force of the fibers in the dyeing and finishing process, the obtained bulkiness is usually restricted, and it cannot be expected to obtain a yarn having a sufficiently high bulkiness.